Google Compute Engine firewall egress rule opened to the world

gcp

Classification:

attack

Tactic:

TA0005-defense-evasion

Technique:

T1562-impair-defenses

Goal

Detect when a Google Compute Engine firewall egress rule is opened to the world.

Strategy

This rule monitors Google Cloud Audit Logs to determine when a v*.compute.firewalls.insert API call is made with the traffic direction as egress (@data.protoPayload.request.direction:EGRESS) and the destination range as all IP addresses (@data.protoPayload.request.destinationRanges:0.0.0.0/0).

An excessively open firewall rule like this could be a sign of an ongoing cryptomining attack.

Triage and response

  1. Determine if {{@usr.id}} from IP address {{@network.client.ip}} should have made the {{@evt.name}} API call.
  2. If the API call was not made by the user:
  • Rotate the user credentials.
  • Determine what other API calls were made by the user.
  • Investigate VPC flow logs and OS system logs to determine if unauthorized access occurred.
  1. If the API call was made legitimately by the user:
  • Advise the user to modify the IP range to the company private network or bastion host.

Changelog

  • 17 August 2023 - Updated query to replace attribute @threat_intel.results.subcategory:tor with @threat_intel.results.category:tor.